We report polymer solar cells (PSCs) based on poly(3-hexylthiophene (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) using water-soluble nickel acetate (Ni(CH3COO)(2), NiAc) instead of acidic poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) as hole collection layer (HCL) between the indium tin oxide (ITO) electrode and photoactive layer. The NiAc layer can effectively decrease R-s and increase R-p and shows effective hole collection property. Under the illumination of AM1.5G, 100 mW/cm(2), the short-circuit current density (J(sc)) of the NiAc based device (ITO/NiAc/P3HT : PCBM/Ca/Al) reach 11.36 mA/cm(2), which is increased by 11% in comparison with that (10.19 mA/cm(2)) of PEDOT : PSS based device (ITO/PEDOT : PSS/P3HT : PCBM/Ca/Al). The power conversion efficiency of the NiAc based devices reach 3.76%, which is comparable to that (3.77%) of the device with PEDOT : PSS HCL under the same experimental conditions. Moreover, NiAc based PSCs show superior long-term stability than PEDOT : PSS based PSCs. Our work gives a new option for HCL selection in designing more stable PSCs. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 684-690, 2013